Fateh all ,
am a sports scientist, and Bulking up is not all about going to the gym and working out you also need to be on a high protein diet and Also a good exercise plan..
I would strongly recommend you to have a word with a PT and ask for some advice, However I will help you get started.
First I strongly recommend you to focus on your diet, find out your body mass index, (BMI), find out how much your recommended daily intake should be..
Secondly to build muscle and maintain weight you must eat at least four small meals a day, which has to consist of a healthy balanced diet, and this is very vital..
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building muscle takes a very long time, low fat milk and soya meat is good sources for protein, eat more fibre, and 5 fruits and 5 veg a day, cut down most fats, so less or no butter in food and plenty plenty of water...
Working out at the gym: remember you need to do a full body work out, 20 to 30mins of cardio could be treadmill, skipping jogging etc, then go on to the machines and free weights, low reps and high weights.
Hope this helps if you need more advice feel free to ask.
Fateh all. .